Syngas fermentation uses acetogenic bacteria to convert CO and H2 to ethanol, via the Wood Ljungdahl pathway to acetic acid and then reduces the acetic acid to ethanol using electrons and protons derived from H2 or CO. Commercial deployment of syngas fermentation is imminent with INEOS Bio completing construction and start-up of an 8 million gal/yr plant in Vero Beach, Fla., and Lanza Tech constructing large facilities in China. Economics of syngas fermentation require                High conversion of both CO and H2 to conserve the energy of the feedstock in the fuel product;        High selectivity of the fermentation to produce ethanol in preference to acetic acid, cell mass or other products; and,        High rates of gas consumption and product formation.        
Additionally, the fermentation must be stable and capable of long-term continuous operation without interruption and process upset. Control of the syngas supply to match the capacity of the bacterial culture to convert the CO and H2 to ethanol or other products is critical.
Previous research has focused on increasing the rate of mass transfer of CO into the fermentation to overcome the low solubility of CO (and H2) in the aqueous fermentation broth. The prejudice that forced high mass transfer is required (more is better) results in inhibition of H2 uptake by accumulated CO in the cells, reliance on CO as the primary driver of production, and low conversion of H2 with resulting low conservation of energy from the syngas.
Typical control for fermentation processes (without known exception) is based on a choice of an operating pH, and adds base and/or acid to maintain the control set point. This decision requires dedicated pH measurement to control the addition of base from separate equipment, including tanks, mixers, pumps, valves and piping. The addition of base is determined by the effect of fermentation controls operating on the basis of chosen flow and conversion targets. These targets are set for poorly defined (arbitrary) reasons and require continuing assessment and adjustment by the operator.
As such, there is a clear need for an approach that does not suffer the disadvantages of the prior art.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.